Amongst the pipes used in a motor vehicle, there are smooth pipes of large diameter presenting bends and which are intended, for example, to form the fuel tank filler pipe. Such pipes are made by blow-molding. Unfortunately, that method of manufacture is relatively expensive. Attempts have been made to make such pipes by extrusion followed by hot-forming, since that method of manufacture is less expensive and also makes it possible to obtain pipes that are lighter than those obtained by blow-molding. However, that method has been found to be difficult because extruded pipes tend to flatten while they are being shaped.
That type of problem is to be found in general manner in all smooth pipes made of plastics material that are shaped in such a manner as to have bends so that their shape matches the environment in which they are to be installed. More particularly, such structures are not suitable for diameters in excess of 25 millimeters (mm) since they are difficult to shape by thermoforming: a smooth pipe of large diameter tends to kink as soon as too small a radius of curvature is imparted thereto.
Attempts have been made to replace such smooth pipes with corrugated pipes which are easier to shape. Nevertheless, such pipes lead to problems of fluids foaming, in particular of fuel foaming, problems of noise, and problems of head loss.
Furthermore, another drawback of the pipes presently in use lies in the fact that it is difficult to obtain permeability to automobile fluids that is low enough to enable them to perform their function effectively. This drawback is particularly harmful in corrugated pipes which present a large surface area in contact with the fluid.
To obviate that drawback, is it known to use multilayer pipes, but they too are relatively expensive.